methods of sterilization

1. STERILIZATION
Presented by
DR HUDA NAFEES
ASSISTANT PROFESSOR
dr.hudanafees@gmail.com

2. STERILIZATION
 Sterilization is making a substance free from all micro
organisms both in vegetative and sporing states.
 Spore is a reproductive structure that is adapted for dispersal
and surviving for extended periods of time in unfavourable
conditions.
 Spores form part of the lifecycles of many bacteria, plants,
algae , fungi and some protozoa.

3. Terms usedin sterilization:
 Disinfection:
The destruction or removal of all pathogenic organisms capable of giving
rise to infection.
Disinfection does not affect spore state organisms.
 Antisepsis:
The term is used to indicate the prevention of infection, usually by
inhibiting the growth of bacteria in wounds or tissues.
This is done by the antiseptics
Chemicals or disinfectants which can be safely applied on skin or mucous
membrane to prevent infection by inhibiting the growth of bacteria.
 Bactericidal agents / germicides:
Those which able to kill bacteria.

4.  Bacteriostatic agents:
Only prevent multiplication of bacteria, but they remain
alive.
 Cleaning:
Important preparatory step before sterilization or
disinfection, by removing soil and other dirt.
 Decontamination:
The process of rendering an article or area free of
contaminants, including microbial, chemical, radioactive and
other hazards.

5. • Dry heat sterilization
• Moist heat sterilization
• Sterilization by radiation
Physical
method
• Gaseous sterilization
• Sterilization by disinfectant
Chemical
method
• Pass through bacteria-proof filter
Mechanical
method
METHODS/AGENTSOF
STERILIZATION

6. DRY HEAT STERILIZATION
Instrument- ‘OVEN’
OVEN : specially designed instrument - electrically heated and thermostatically
controlled. Expose at 160 ºC for 1 hour.
Advantages :
1. it is suitable method for sterilization of substances destroyed by moisture.
2. They do not require water and there is not much pressure build up within the
oven, unlike an autoclave, making them safer to work with.
3. Suitable to be use in a laboratory environment.They are much smaller than
autoclaves but can still be as effective.
Disadvantage:
As they use dry heat instead of moist heat, some organisms like prions, may not be
killed by them every time.

8. MOIST HEAT STERILIZATION
 Instrument- ‘AUTOCLAVE’
 Heating process in autoclave - saturated steam under
pressure is allowed to penetrated through materials for 15
minutes and temperature 121º c.
Advantage:
micro organism are killed most efficiency in lesser time due
to high pressured saturated steam
Disadvantage:
unsuitable for materials not withstanding temperature of
115ºC or more during heating

10. STERiLIZATION BY RADIATION
 Two techniques involved:
 Alteration of chemicals lead to form new compound in cells
destroying the micro-organism itself
 Vital structure like nuclear protein are destroyed killing the micro-
organism.
 e.g., Co-60 - used for gamma ray sterilization process.
2 types of radiation:
 Ionising radiation
 Non-ionising radiation

11. Ionising radiation Gamma rays:
 X-rays: Used for sterilising plastics, syringes,
 Gamma rays –
generally obtained from radio isotope(Co-60) during disintegration of unstable
atoms
kill micro-organisms by isolating atoms of essential substance of cells present in
them
ADVANTAGE :
1. No significance rise in temperature
2. Continuous process due to short exposure time.
DISADVANTAGE :
1.May lead to color change.
2. Solubility of preparation leading to decomposition of certain materials.

12. Non-ionising radiation
 Infrared-Used for rapid mass sterilization of prepacked items
such as Syringe,Cathaters
 UV : Used for disinfecting enclosed area such as entryways,
operation theatres and labs.
Testing - Efficacy of Radiation:
Radiation control indicator disc: Special paper sticker which is
yellow in colour, is sticked on the articles. After proper sterilization
disc colour changes to red.

13. Chemical methods of Sterilization
 Chemical agents:
 Action of chemical agents:
i. Protein coagulation
ii. Disruption of cell membrane resulting in exposure,
damage/loss of contents
iii. Removal of sulfhydryl group essential for normal
functioning of enzyme
iv. Substrate competition.

14.  Commonly used chemical :
Alcohol
a. Ethyl alcohol ,Isopropyl alcohol
b. These must be used at concentration 60-90%.
c. Isopropyl alcohol used in disinfection of clinical thermometer.
d. Methyl alcohol is effective against fungal spores, treating cabinets and
incubators.
e. Methyl alcohol is also toxic and inflammable.
Aldehyde
I. Formaldehyde:
 Having Bactericidal, sporicidal and has lethal effect on viruses.
 Used to preserve anatomical specimens, destroying anthrax spores on hair
and wool.

15. II .Glutaldehyde:
Effective against tubercle bacilli, fungi, viruses.
Less toxic and irritant to eyes, skin
Used to treat anaesthetic rubber, face masks, plastic endotracheal
tubes, metal instruments and polythene tubing.
Dyes:
2 groups of dyes:
1.Aniline dye 2.Acridine dye
 Both are bacteriostatic in high dilution but are of low bactericidal
activity.
 Aniline dye is more active against gram +ve than gram-ve
organisms.

16.  Some important dyes:
 Proflavine Acriflavine Euflavine Aminacrine
 These Impair the DNA complexes of the organisms and thus kill
or destroy the reproductive capacity of the cell.
Halogens
Iodine :
 Used as Skin disinfectant
 Having Active bactericidal activity &moderate action on spores.
Chlorine :
 Used to disinfect Water supplies, swimming pools and food and
dairy industries.
 Along with hypochlorides are bactericidal. Also act on viruses.

17. Phenols :
 These are obtained from distillation of coal tar between 170-270
C.
 Lethal effects are:
a. Capacity to cause cell membrane damage, releasing cell
contents and causing lysis.
b. Low concentration will precipitate proteins.

18. Gases:
Types of gases used for sterilization:
i. Ethylene oxide
ii. Formaldehyde gas
iii. Beta propiolactone (BPL).

19. Ethylene oxide:
 The gas used is safe & non-inflammable.
 Now-a-days, ethylene oxide most widely used gaseous sterilization
agent in medical science.
 Action is due to its alkylating the amino, carboxyl, hydroxyl and
sulphydryl groups in protein molecules.
 Also on DNA and RNA.
 Items: heart-lung machines, respirators, sutures, dental equipment,
books, clothing.
 Advantages: It has penetration power quite useful for sterilizing
surgical instruments (such as catheter, needles, plastics, disposables)
 Disadvantages:
1. Very slow sterilization process
2. Very costly equipment

20. Formaldehyde gas:
 This is widely employed for fumigation of OT and other rooms.
Formaldehyde is produced by adding 150g of KMnO4 to 280ml of
formalin for every 1000cu.ft of room volume, after closing the
windows and other outlets.
 After fumigation, the doors should be sealed and left unopened for
48 hours.
Betapropiolactone:
 Product of ketone and formaldehyde with a boiling point of 163 C.
 Having rapid bactericidal activity but carcinogenic.
 Capable of killing all microorganisms and is very active against
viruses.

21. DISINFECTION
 Decontamination - removal of microorganisms
contaminating an object
 Preservation - preventing methods of microbes-caused
spoilage of susceptible products(pharmaceuticals, foods)
 Sanitization - removal of microbes that pose a threat to
the public health, food industry, water conditioning
 sanitizer-an agent, usually a detergent, that reduces the
numbers of bacteria to a safe level

22. MECHANICAL METHOD
 The solution to be sterilized is passed through depth filter or
screen-filter which includes:
I. Particulate filters
II. Microbial filters
III. Final filter
 Pharmaceutical solutions are sterilized by this method.
 The micro-organism are physically removed by absorption on the
filter medium or by mechanism.
 Sterilization test must be done.